The present invention relates to an injection-molding machine controlled by means of a numerical control unit (hereinafter referred to as NC unit), and more particularly, to a numerical control method for an injection-molding machine and an apparatus therefor, capable of executing a mold opening process simultaneously with a metering process.
In an injection-molding cycle, a metering process and a mold opening process are executed subsequent to an injection process and a hold process. The metering process can be started immediately after the completion of hold, while the mold opening process can be started after solidification of resin injected into a mold, that is, after the passage of a cooling period. Usually, the cooling period is shorter than a metering time, so that the cycle time for the manufacture of moldings can be shortened by opening the mold immediately after the termination of the cooling period.
In injection-molding machines using oil pressure as a drive source, various axes, such as an injection axis, metering axis, clamp axis, eject axis, etc., can be controlled independently and simultaneously. Therefore, mold opening is started the moment the cooling period terminates during the metering process, that is, metering operation and mold opening operation are executed simultaneously. According to injectionmolding machines in which the drive of servomotors for their axes is controlled by means of an NC unit, on the other hand, it is difficult for the NC unit to control a plurality axes simultaneously and independently, due the limited computing capability of the NC unit. Accordingly, the mold opening operation is performed after the metering operation is finished. Thus, the prior art injection-molding machines controlled by means of an NC unit require a long cycle time, and therefore, are low in production efficiency.